Ok so I have a heap of oil all over the back rim which is coming off the chain. I also have some coming out of the left side and building up on the fin around the spark plug. It seems all this can be linked back to the breather box. There were at least three variations to the breather box and yamaha never seemed to get this right from what I have been reading. Originally it had the larger box with 2 outlets, later the sealed one of those outlets and just ran one hose. Later on they went to the smaller box with a single narrow outlet which I hear was too restrictive.
I have excessive oil which could mean it is overfilled (see note on wrong capacities lower down) but I doubt this as the bike hasn't had an oil change since I got it. It is on the to do list. So there is a possibility that the baffles/fins are gummed up. Also worth noting that mine is a 74 with the larger box and one hose running down to oil the chain. It is just getting far more oil than it should. The second un used nipple is filled with what looks like silicon. If it is and the PO was a bit over zealous with the silicon there could be the source of a blockage.
My intention is to machine up a new single nipple and swap it for the twin stock nipple. When removed inspect the baffles.
Restrictive (short) late style breather (left) and the low restriction early model long dual outlet breather (right), it has two 3/8 inch outlet holes and a double the stock size oil separator metal baffle hole inside. This big assembly causes carb mounting interference problems and Yamaha discontinued it, but the smaller replacement design it not big enough for a stock motor, much less a bored, performance tuned or stroked motor.
The small holes in the stock breather housing and stock baffle plate shown above can cause the cam chain tensioner rectangular cover gasket, the cylinder base gasket, the clutch push rod seal, and the countershaft output shaft seal to blow and or seep or leak oil due to excessive crankcase pressure.
On the early models the breather vent emptied out over the chain, helped keep it oiled. Obviously the will be some oil/mist leakage on an engine with excessive wear/blowby. As the years went by they changed the breather system. The epa didn't like oil blowed all over. They ended up with the breather vented into the airboxes and sucked into the engine to be burnt.
Some guys are putting filters, oil tins, etc to catch the misted oil. Others are putting in a break valve. You can't use a PCV valve because they have a ball bearing in them and it won't move fast enough at higher RPMs. Basically, the thing won't function. Needs to be the reed or flap type.
however...you WILL get positive pressure however slight in a well sorted motor if you remove your original airbox and fit pod filters.
After weeks of research and exchanging emails with a guy in Australia who is an expert on crankcase breathing in many different types of engine I learnt the issue...
We run a motor that has two pistons that arrive at the top both at once, causing no natural equalization of pressure. They are two quite large pots in a small space...taking off the induction breather system means that the original breather system now becomes a slight restriction...so just fitting a straight through breather system becomes say 50% effective in comparison to the inducted breather...
Natural blow by (which is unavoidable even in the most well sorted new engine) means that there is always more energy causing positive pressure than there is negative. Therefore with a straight through breather that has the same resistance to output as input you get positive pressure whether you like it or not.
The ONLY way round this is to fit the airbox back...OR..to fit very very freeflowing one way valves..
The airbox is smell free because its a sealed circuit...and lets say this is 100% effective as mostly it is...if thats try a well sorted one way valve setup is say 80% effective ...but it still smells.
I had a leak from my cam caps..(what I call them) and fitting the one way valve from Mikes which is easily opened...fixed it ..straight away..
Before that I had break servo valves that allowed too much positive pressure build before they opened..
Mikes valve is a fast moving light flap of material ..
Interesting side note on the oil levels the book says to check oil warm, on the center stand, let set a few minutes, remove dipstick wipe clean, set back in hole with dipstick just setting on threads, not screwed in. This is a problem for me as I don't have a centre stand!!!!
Never heard anyone mention steel wool before, is it correct from factory??
|Not 100% sure if this baffle should have the hole to the top or bottom. I think it is the bottom or the 90Deg. piece on the back ends up in the middle of the nipple on re assembly. Clarification on this would be appreciated.|
The breather box that attaches to the cylinder head has some strange baffle system to separate oil from the "breath" and return it to the engine.
So for me I will get some stock to machine a single nipple, get the baffles in, without steel wool, and swap this on to the bike and the redo the take off for the 76. I will try and check the oil level to mid point on the dipstick. Then reassess as to if I want to add the valve in.